Crushing combined with high-frequency turning can promote material degradation of sheep manure compost on the Qinghai-Tibet Plateau by improving the microbial metabolic function

Large sheep farms on the Qinghai Tibet Plateau (QTP) can produce a large amount of sheep manure annually. However, the sheep manure in this area has hard particles and high lignocellulose content, which leads to low composting efficiency and uneven internal and external fermentation. This study aimed to explore the effect of crushing pretreatment on the organic components, antibiotics degradation, and the microbial metabolic functions of sheep manure composting in the QTP. The experiment set up the turning treatments once every 2 d (CT2) or once every 4 d (CT4) after crushing pretreatment. A protocol of no crushing and turning once every 4 d was used as the control (CK). The results showed that compared with CK, CT2 could increase the organic matter degradation rate by 22.5 %, increase the humus content and germination index by 18.9 % and 14.3 %, while CT4 had no obvious effect. CT2 can effectively promote the elimination of tetracycline and beta-lactam antibiotics and increase their elimination rate by 7.9-19.3 %. CT2 increased the abundance functional genes involved in carbohydrate metabolism, amino acid metabolism, energy metabolism, cellulolysis, xylanolysis, and chitinolysis of bacteria, and increased the functional genes abundance of carbohydrates, proteins, lipids, and nucleotide metabolism in fungi. Furthermore, several functional enzymes, such as protease and cellulase showed the highest activity in CT2. In conclusion, crushing pretreatment and turning once every two days have the best composting effect.